Instrument of precision



July 19, 1938. F. vANcuRA- INSTRUMENT OF PRECISION Filed Sept. 8, 193'?` R m m .Vm am 5M ATTORNEYS Patented July 19, 1938 UNi'rsn stares PATENT OFFICE f 2 Claims.

This invention relates to instruments of precision and consists in means for effecting and for measuring minute adjustment of two relatively rotatable plates. Of wide and general ap- 'p1icabi1ity, it finds immediate utility in the construction of protractors, and in that application it will here be shown and described.

In the accompanying drawing Fig. I is a View in plan of a protractor that embodies the inven- 1 Ation; Fig. II is a fragmentary view in elevation, and in Fig. I the field of View and the direction that afford the showing of Fig. II are indicated at II-II Fig. III is a fragmentary view in sec- .tion, on the plane indicated at III-III, Fig. I; 1 "and Fig. IV is a fragmentary view in plan and to larger scale.

'Ihe protractor includes, as is usual, two straight edges, I and 2, severally mounted on A disks 3 and 4. The two disks are concentrically "pivoted for relative Irotation, and a clamping screw 5 is provided for securing the two disks in any position of angular displacement to which they may be brought. The underlying disk 3 is larger than the overlying disk 4 by a sufficient 255 margin; and the margin of the underlying disk is graduated as shown, to form a scale. The overlying disk 4 is bevel-edged, and bears at its edge a radially extending index line, a. The structure and the graduation of the margin of are such and so correlated that the index line upon disk 4 by its position along the circumferentially extending scale upon the margin of disk 3 affords measure of the angularity at which the two straight edges I and 2 stand related. In'the position shown in Fig. I, for example, the reading, 30, tells that thestraight edges are inclined to one another at an angle of 30. v

It is usual in these instruments to graduate the margin of the disk 3 to degrees, as the disk here is shown to be graduated, but not more minutely; and, in order to measure with greater precision the infinitely variable angle at which the straight edges may stand, it is usual to form upon the beveled edge of disk 4 a Vernierv scale. In the instrument of this invention a Vernier is not employed, butv instead a renement of structure is provided, in consequence of which the angularity of the straight edges may readily be measured in minutes and even in seconds.

'Ihe overlying disk 4 is elaborated in structure. It consists of two concentrically mounted'and relatively rotatable parts: the disk 4 of the familiar instrument, with its index line a, and an incomplete disk or plate 6 superposed on plate disk 3 and the positioning of the index line a.

4. This plate 6 carries immediately the straight` edge 2. The margin of plate 6 is, throughout a sufficient interval, shaped to the arc of a. circle of smaller radius than that of disk 4, and this arc-shaped margin of plate Ii is beveled and bears a radially extending index line b'. It is advantageous also to provide upon the vedge of disk 4, in addition tothe index line a, the radial lines c and d, spaced laterally upon the two sides of line a at intervals that indicate `a range ofswing of one degree each way of plate 6i upon jdiskl 4.'

Through a slot I in plate 6 remote from thecentre extends a clamping screw 8 by which vthe plate 6 is normally clamped to and integrated with thedisk 4. So long as the screw is tight, the instrument is serviceable as an ordinary protractor. It is `only when the screw is loosened that the disk 4 and plate 6 are released for relative rotation and for the operation of parts in which my invention particularly lies.

The disk 4 and the plate 6 are slotted with elongate, parallel-Walled slots 9 and IB.' The slots arev of equal length and in theassernbly` are approximately coincident in position, and, they are approximately radial in their extent.

The departure from precisely coincident posi-vr tion is indicated in Fig. IV.` Their axes extend at a slightangle one to the other. A cylindrical block II of a diameter equal to slot width extends into eac-h slot. Because of the angularity in the placement of the slots a shifting of the block II in radial direction with respect to the centre of relative turning of disk and plate eiects angular displacement of plate 6 relatively to disk 4. The slots are so arranged and proportioned that within the range of movement of block II the displacement of the plate 6 may amount to as much as one degree.

Means are provided for a gradual and controlled shifting of block I I along the slots. Such means are found in a nut I2 that travels upon a threaded shaft I3. The shaft I3 is rotatably mounted in radial position in bearingsv carried by plate 6 and is provided with a milled head I4 which it may be turned manually. The nut I2 carries pivotally the block Il. As the shaft is turned the block is shifted. Upon the adjacent surface of plate 6 two graduated scales are laid (Fig. I), and upon the outspread foot of the sliding nut I 2 an index line for each scale is laid. f

While a single scale and index line will suflice, two scalesl simplify operation in some cases-the calibrations on one scale reading upward in right-to-left direction and the calibrations on the other reading in opposite direction. Each scale iti:

is conveniently formed of sixty graduations; and the proportions and organization are such that the line and scale afford index in minutes of the swing of plate 6 upon the disk 4.

The threaded connection between nut I2 and shaft I3 may be so proportioned that with each rotation of the shaft plate 6 is shifted one minute. The flat face of head I4 of the shaft may be scaled peripherally with sixty graduations (Fig. II), and, cooperating with this scale, index line b upon plate 6 may then additionally afford reading of seconds in the range of shift of plate 6 upon disk 4.

The use is that of a protractor of ordinary structure, with this refinement. Let it be supposed that the angle is to be measured at which two lines lie upon a drawing. Screw 8 is initially tight, with line b coincident with line a, the line` upon nut I2 coincident with zero of the scale upon plate 6, and zero of the scale upon head I4 coincident. with line b. Screw 5 is initially loose. Straight edge I is laid on the drawing in coincidence with one of the lines, and disk 4 is turned until straight edge 2 comes to coincidence with the other. Screw 5 then is tightened. Conceivably line a upon disk 4 may then be found to be coincident with a graduation line in the scale upon the margin of disk 3, and in such case no further mensuration is needed-the angle is of so many degrees value. If, however, as ordinarily will be the case, the line a is found in intermediate position between two graduations of the scale, screw 5 is made tight, screw 8 loosened, and shaft I3 turned. The shaft is turned until the line b comes to coincidence with the next lower line upon the scale ef disk 3 than the point at which line a has come to rest. The readings of the scales upon the plate 6 and upon the head I4 will then give the minutes and seconds by which the angle under mensuration exceeds the number of degrees now indicated by line b with respect to the scale upon disk 3.

Manifestly, by opposite shifting of the nut I2 upon the shaft i3 (assuming the initial setting to be such as to permit opposite shifting) the interval may be measured in minutes and seconds, by which the line a in its position falls short of the next higher degree mark.

By the means described the straight edges I Y and 2 may be set in any required relative positions of angularity, within the capacity indicated.

The invention is manifestly applicable to instruments of precision generally in the making of measured angular adjustment.

I claim as my invention:

1. In a protractor that includes two straight edges and two disks coaxially mounted and relatively rotatable, a refinement of structure adapted to afford more accurate mensuration, such refinement consisting in a plate mounted for rotation on the common axis of the two disks, the said plate carrying integrally one of the two straight edges, means for alternately securing the plate for integral rotation with or releasing it for independent rotation with respect to the immediately adjacent disk, the more remote disk being the one that carries the other straight edge, the said plate and the disk immediately adjacent to it being slotted with parallel-sided slots that extend in' general radial direction with respect to the axis of turning but having in the assembly mutual Obliquity of position, and a block engaging at once the parallel sides of both slots and movable while so engaged longitudinally of both slots and radially with respect to the axis of turning.

2. In a protractor thatI includes two straight edges and two disks co-axially mounted and relatively rotatable, a refinement of structure adapted to afford more accurate mensuration, such refinement consisting in a plate mounted for rotation on the common axis of the two disks, the said plate carrying integrally one of the two straight edges, means for alternately securing the plate for integral rotation with and releasing it for independent rotation with respect to one of the two disks first named, the second of the two disks first named being the one that carries the other straight edge, the said plate and the first of the two disks first named being slotted with parallel-sided slots that extend in general radial direction with respect to the axis of turning but having in the assembly mutual Obliquity of position, and a block engaging at once the parallel sides of both slots and movable longi tudinally of the so engaged slots and radially with respect to the axis of turning.

FRANK VANCURA. 

